In the conventional known Venetian blind production as shown in FIG. 1, a pair of ladder cords 3a, 3b are mounted between a head box 1 containing stopper means or mechanism for the slat ascending and descending cords (hereinafter referred to as slat up-down cords) and operating means for slat keeping and slanting ladder cords, and a bottom rail 2, in advance, said head box 1 is provisionally secured at a position where said bottom rail 2 does not contact a floor at site, and thereafter an workman lays down each slat on each suspension tape 5 of the ladder cords 3a, 3b at both sides in a ladder configuration, by his hands, and then he inserts and passes the slat up-down cords 6a, 6b through through holes 7a, 7b which are provided near the both ends of the slat 5 so as to attach tip end of the cords to the bottom rail 2, so that the blind is assembled.
However, the slats 5 is formed of a thin metallic sheet which is curved on which painting agent is coated and these are some times of 3-4 meters at each length. Hence, there have been provided numerous ladder cords to support such slats and each laying down of the slat on each of the suspension tape of the ladder cords by manual operation of the worker. Thus, it takes a considerable long time for such work and often two workmen should work in each pair for such job when the slats are relatively long. The recent higher cost and salary for the workers and such mode of the job with such assembling device will cause the higher cost and long assembling time which lead the incompetent products in the market.